Electrochemical/photoelectrochemical water-splitting is widely considered to be an important step towards efficient renewable energy production, storage, and usage such as rechargeable metal-air batteries, fuel cells, and especially sustainable hydrogen production. Currently the state-of-the-art catalysts to split water are iridium (Ir) and platinum (Pt) for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) respectively, with about 1.5 V to reach 10 mA/cm2 current (for integrated solar water-splitting). However, the price and scarcity of these noble metals present barriers for their scale-up deployment. A great deal of effort and progress have been made towards efficient OER and HER catalysts with earth-abundant materials, such as cobalt phosphate, perovskite oxides, and transition metal oxides/layer-double-hydroxides for OER, and transition metal dichalcogenides and nickel molybdenum alloy for HER. However, combining different OER and HER catalysts together in an integrated electrolyzer for practical use is difficult due to the mismatch of pH ranges in which these catalysts are stable and remain most active. In addition, producing different catalysts for OER and HER involves different equipment and processes, which could increase the cost.
Therefore, developing a bifunctional electrocatalyst with high activity towards both OER and HER in the same electrolyte remains challenging.